| the curve of the wave itself | transverse wave; this is the actual position of the string while the wave is travelling through it |
| the horizontal line | equilibrium position; this is a line drawn for reference. It represents where the string would be without a wave travelling through it. |
| crest | highest point of the wave |
| trough | lowest point of the wave (pronounced "troff") |
| amplitude (A) | This is the size of the wave, it is the height of the crest or the depth of the trough measured from the equilibrium position |
| wavelength (λ) | The distance measured from crest to crest, from trough to trough, or from any point in the wave until it repeats itself exactly. |
| reference point (P) | One location on the string |
An observer watching point "P" carefully as the wave moves by would note that the point would rise to a maximum height at the crest of the wave, and would then fall to a maximum depth at the trough of the same wave. After the wave passed, the point would return to the equilibrium position. When another wave would pass the observer, the process would repeat itself. This type of repetitive back-and-forth motion is called oscillatory.
The time in seconds it takes for one complete wave to move past a point is called the period (T). A closely related concept is the frequency (f) of the wave, which is the number of waves per second that pass a given point.
The equation that relates period and frequency is: f = 1 T
For example, if 0.1 seconds go by as one complete wave passes point P, the period of the wave is 0.1 seconds, and the frequency of the wave is 1 T = 1 0.1 = 10 waves/second or 10 Hertz.